text: In all cases where  decay (positron emission) of a nucleus is allowed energetically, so too is electron capture allowed. This is a process during which a nucleus captures one of its atomic electrons, resulting in the emission of a neutrino:
  An example of electron capture is one of the decay modes of krypton-81 into bromine-81:
  All emitted neutrinos are of the same energy. In proton-rich nuclei where the energy difference between the initial and final states is less than 2,  decay is not energetically possible, and electron capture is the sole decay mode.
  If the captured electron comes from the innermost shell of the atom, the K-shell, which has the highest probability to interact with the nucleus, the process is called K-capture. If it comes from the L-shell, the process is called L-capture, etc.
  Electron capture is a competing (simultaneous) decay process for all nuclei that can undergo β decay. The converse, however, is not true: electron capture is the only type of decay that is allowed in proton-rich nuclides that do not have sufficient energy to emit a positron and neutrino.